Check the credits for links, but basically Incompetech and OpenGameArt. I trimmed "Gary"'s gun handling noises down to get that nice solid "click", but didn't have to do anything else to it. It worked perfectly! (In my opinion.)
Well I caved and ran a modern web browser to play it, and it was a fun bouncy experience
Appreciate you trying it out! Hopefully the measures required were not excessively heroic... ; - )